1. Field of the Invention
The present invention relates to a system for treating water used in the fabrication of semiconductor devices. More particularly, the present invention relates to a photo-oxidation device for oxidizing organic material contained in the water with UV (Ultra Violet) radiation, to a water treatment system equipped with the photo-oxidation device, and to a method of treating water comprising a step of irradiating the water with UV radiation to oxidize organic material contained in the water.
2. Description of the Related Art
Generally speaking, large amounts of water are used to clean semiconductor substrates and the like when fabricating semiconductor devices. The water is either municipal water or water which has already been used in the manufacturing line. Such water, however, must first be treated by a water treatment system.
The water used in the semiconductor device fabrication process is deionized water from which suspended particles, organic material, and ions, etc. have been completely removed. The deionized water is generally prepared by subjecting untreated water to a pre-treatment such as precipitation, followed by reverse osmotic pressure, photo-oxidation (using UV), and ion-exchange treatments.
The photo-oxidation treatment oxidizes the organic materials contained in the water. Specifically, a UV-lamp is used for irradiating the water with UV radiation of a certain wavelength. Then the water containing the oxidized organic materials is subjected to an ion-exchange treatment.
Referring to FIG. 1, the conventional photo-oxidation device comprises a UV-lamp 10 and a photo-oxidation section 12 including a line through which the water flows. The photo-oxidation is used to treat the micro-organic materials which were not removed by the other pre-treatments. When the water flowing through the photo-oxidation section is irradiated with UV radiation having a certain wavelength, these organic materials react with the UV radiation by oxidizing (photo-decomposition) into organic acid ions having a composition such as CO.sub.2 or HCO.sub.3. An ion-exchange treatment then uses H.sup.+ or OH.sup.- to neutralize the organic acid ions.
However, aromatic organic materials, which are relatively stable chemical compounds, cannot be completely oxidized using the conventional photo-oxidation instrument. That is, UV radiation alone cannot cause aromatic organic materials to decompose into organic acid ions. Accordingly, water containing aromatic organic materials is supplied to the semiconductor device fabrication line. Because recent semiconductor fabrication processes are sensitive to organic materials on the order of ppb (Parts Per Billion) in the water, water containing aromatic organic materials may cause significant production failures. That is, the reliability and the yield of the semiconductor devices are adversely affected.
Furthermore, the water-treatment system operates continuously in an attempt to treat the water as completely as possible. This contributes to increased manufacturing costs.